Middle phase continuously variable valve timing system with intermediate lock pin and cam torque response control and method thereof

ABSTRACT

A method of controlling an intermediate lock pin and cam torque response for a continuously variable valve timing system with is disclosed. The method includes entering a cam phaser control mode for controlling the middle phase CVVT when an engine starts, or performing lock pin chattering of a lock pin locking a cam at a middle position which is between an advanced position and a retarded position, by an oil pressure. A cam torque response control mode for controlling the middle phase CVVT is entered. The lock pin chattering occurs due to an intermittent oil flow supplying to the lock pin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Korean Patent Application No. 10-2014-0078259, filed on Jun. 25, 2014 which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a continuously variable valve timing system, and more particularly, relates to a middle phase continuously variable valve timing system with intermediate lock pin and cam torque response control.

BACKGROUND

Due to increasing demand for fuel efficiency improvement, exhaust gas reduction, low-speed torque increase, and output improvement, there is a need to improve performance of a continuously variable valve timing system (CVVT) or camshaft phaser system capable of optimally controlling intake/exhaust valve opening and closing timing thereof according to an engine revolutions per minute (RPM).

To improve the performance of the conventional CVVT, a middle phase CVVT has been developed to reduce a system responsiveness time and to expand a cam operating range.

The middle phase CVVT improves the fuel efficiency by increasing a valve overlap of intake and exhaust valves to reduce a pumping loss, and reduces the exhaust gas by using an internal exhaust gas recirculation (EGR) re-combust combustion gas from the valve overlap according to engine conditions. The middle phase CVVT further improves the low-speed torque and the performance thereof by increasing volume efficiency using optimization of intake valve timing according to the engine conditions, thereby further improving the fuel efficiency and the exhaust gas reduction.

The middle phase CVVT controls a cam position at a middle position, neither at the retarded (intake) position nor the advanced (exhaust) position, when controlling middle phase CVVT based on a difference between a target value and a current value of the cam, thereby reducing the system responsiveness time and expanding the cam operating range.

However, the middle phase CVVT maintains a cam middle phase by using a lock pin, and therefore, a delay of unlocking [locking→unlocking] of the lock pin may occur.

For example, the lock pin needs to be rapidly unlocked at all times when controlling the middle phase CVVT, but the unlocking of the lock pin is delayed under a specific condition that an engine RPM is reduced to about 500 RPM to 1000 RPM and an engine oil temperature is about 110° C. to 130° C., and thus, a response delay occurs.

The response delay of the lock pin mainly occurs when the middle phase CVVT is controlled under the condition of an open loop response time (OLRT) at 100° (crank angle)/sec after an engine initiates, thus decreasing efficiency of emission effect which reduces harmful substances.

The middle phase CVVT is regulated to satisfy operation functions at an oil temperature of −10° C. to 130° C. and an engine RPM equal to or more than 500 RPM, such that the response delay of the lock pin under specified low-speed and high-temperature conditions may reduce reliability of the operational performance of the middle phase CVVT.

SUMMARY

An aspect of the present inventive concept is directed to a middle phase continuously variable valve timing (CVVT) system with intermediate lock pin and cam torque response control and a method thereof for reducing a response delay of a lock pin under a condition of an open loop response time (OLRT) at 100° (crank angle)/sec, an engine RPM equal to or less than 1000 RPM, and an oil temperature of 110° C. to 130° C. by using two control modes. The two control modes include a cam phaser control mode as a general control mode and a cam torque response control mode rapidly unlocking the lock pin prior to the cam phaser control mode after a necessity of rapid unlocking switching (lock→unlock) of the lock pin which locks a cam at a middle position when an engine is running, and required operation functions at an oil temperature of −10° C. to 130° C. and an engine RPM equal to or more 500 RPM are satisfied.

Other objects and advantages of the present disclosure can be understood by the following description, and become apparent with reference to embodiments of the present inventive concept. Also, it is obvious to those skilled in the art to which the present disclosure pertains that the objects and advantages of the present inventive concept can be realized by the means as claimed and combinations thereof.

In accordance with an embodiment of the present inventive concept, a method of controlling an intermediate lock pin and cam torque response for a middle phase continuously variable valve timing (CVVT) system is disclosed. The method includes entering a cam phaser control mode for controlling the middle phase CVVT when an engine starts, or performing lock pin chattering of a lock pin locking a cam at a middle position, which is between an advanced position and a retarded position, by an oil pressure. A cam torque response control mode for controlling the middle phase CVVT is entered. The lock pin chattering occurs due to an intermittent oil flow supplying to the lock pin.

The intermittent oil flow may be formed by intermittently turning on/off an oil-flow control valve (OCV) which controls the oil.

The cam torque response control mode may be entered when a target value of the cam is the same as a current value of the cam, and the cam phaser control mode may be entered when the target value of the cam is different from the current value of the cam.

An execution condition of the cam torque response control mode may include an engine revolutions per minute (RPM) of 500 to 1000 RPM and an oil temperature of 110° C. to 130° C.

The execution condition of the cam torque response control mode may further include an open loop response time at 100° (crank angle)/sec for an emission effect.

The cam torque response control mode may be executed by determining whether an unlocking of the lock pin is delayed by a first fast unlocking condition. Whether the lock pin chattering is performed by a second fast unlocking condition after the unlocking delay of the lock pin is determined. The lock pin chattering is performed by controlling the cam torque response control when controlling the middle phase CVVT.

The first fast unlocking condition may include an oil temperature, an engine RPM, and a voltage.

Determination conditions of the first fast unlocking may include oil temperature>TH_(—)0 (oil temperature threshold), engine RPM<TH_R (engine RPM threshold), and voltage<TH_L (voltage threshold). The unlocking delay of the lock pin may be determined when all the determination conditions are satisfied.

The oil temperature may be 110° C. to 130° C., the engine RPM may be 500 RPM to 1000 RPM, and the voltage may be a voltage of an oil-flow control valve controlling the oil of the middle phase CVVT.

When any one the determination condition of the oil temperature, the determination condition of the engine RPM, and the determination condition of the voltage is not satisfied, the unlocking delay determination of the lock pin may terminate, and the cam phaser control mode immediately performing the control of the middle phase CVVT may be entered.

The second fast unlocking condition may include crank signal synchronization, an opening timing determination of the intake valve for each cylinder, a cam torque determination, an oil temperature check, and a cam torque phase determination. When the cam torque phase is a negative cam torque generated and the intake valve is opened, the lock pin chattering may be determined. The oil temperature may be divided into a first oil temperature of a region of 110° C. and a second oil temperature of a region of 130° C., and the lock pin chattering may be performed at the first oil temperature and the second oil temperature, respectively.

When a positive cam torque is generated and the intake valve closes, the lock pin chattering may terminate, and the cam phaser control mode immediately performing the control of the middle phase CVVT may be entered.

In the cam torque response control, the lock pin chattering may be a pulse width modulation (PWM) duty signal supplied to an oil-flow control valve (OCV). The generation of the PWM duty signal may be divided into a first oil temperature of a region of 110° C. and a second oil temperature of a region of 130° C. under the second fast unlocking condition, and an output of the PWM duty signal may be generated at a negative cam torque phase when the intake valve opens under the second fast unlocking condition.

In accordance with another embodiment of the present inventive concept, in a continuously variable valve timing system with inventive concept, a middle phase continuously variable valve timing system includes a controller configured to control a middle phase CVVT when an engine runs. The controller includes a cam torque sensor, a cam phaser control determiner, a cam torque control determiner, and a cam phaser controller. The cam torque sensor is configured to use a crank signal, a cooling water temperature, and an oil-flow control valve (OCV) value as cam torque sensing data, configured to detect a cam torque phase by a negative cam torque generated at the time of opening an intake valve and a positive cam torque generated when the intake valve closes, and configured to output a signal of the negative cam torque to the cam phaser controller. The cam phaser control determiner is configured to use a difference between a cam target value and a cam current value calculated from the cam torque as cam phaser control data and outputs a signal depending on the difference between the cam target value and the cam current value to the cam phaser controller. A cam torque control determiner is configured to use an oil temperature for oil temperature data, configured to divide the oil temperature into a first oil temperature and a second oil temperature, and configured to output the divided oil temperatures to the cam phaser controller. The cam phaser controller is configured to output a pulse width modulation (PWM) duty signal generated by the first oil temperature and the second oil temperature when the cam torque phase is a negative phase and configured to output the PWM duty signal to the OCV controlling an oil of the middle phase CVVT.

The OCV may be connected to an oil pressure circuit, and the oil pressure circuit is connected to the cam which controls an intake valve and an exhaust valve, the oil pressure circuit may be provided with a lock pin locking the cam at a middle position between a most retarded position and a most advanced position, and lock pin chattering may be generated in the lock pin by repeatedly turning on/off the OCV by the PWM duty signal.

The OCV may control the oil at an oil temperature of −10° C. to 130° C. and an engine RPM equal to or more than 500 RPM.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show flow charts of an intermediate lock pin and cam torque response control method for a middle phase continuously variable valve timing (CVVT) system in accordance with an exemplary embodiment of the present inventive concept.

FIG. 2 shows diagrams illustrating an example of a cam torque diagram checked when controlling a dual middle phase in accordance with an exemplary embodiment of the present inventive concept.

FIG. 3 shows a configuration illustrating an example of lock pin chattering by a cam torque response control mode divided from a cam phaser control mode during the dual middle phase control in accordance with the exemplary embodiment of the present inventive concept.

FIG. 4 shows a diagram of responsiveness greatly improved by lock pin chattering under a condition of an open loop response time (OLRT) with 100° (crank angle)/sec, an engine RPM equal to or less than 1000 RPM, and an oil temperature of 110° C. to 130° C. in accordance with an exemplary embodiment of the present inventive concept.

FIGS. 5A and 5B show configuration examples of a middle phase CVVT system controlled by a controller to perform cam torque response control in accordance with the exemplary embodiment of the present inventive concept.

DETAILED DESCRIPTION

FIGS. 1A and 1B, 2, 3, and 4 illustrate an example of a middle phase continuously variable valve timing (CVVT) system with intermediate lock pin and cam torque response control and a method thereof.

Referring to FIGS. 1A and 1B, an intermediate lock pin and cam torque response control method for a middle phase continuously variable valve timing system includes sensing a cam torque when an engine starts (S10) and determining a difference between a target value and a current value of a cam (S20). A cam phaser control mode is entered when the difference between the target value and the current value of the cam occurs (S200 and S300), and a cam torque response control mode is entered (S30 to S140) when there is no difference between the target value and the current value of the cam. In this case, the occurrence of the difference between the target value and the current value of the cam represents a predetermined time period after an initial starting of the engine, and the non-occurrence of the difference between the target value and the current value of the cam represents the initial starting of the engine or an idle of the engine. Therefore, the determination on the cam torque response control mode is performed soon after a controller for the middle phase CVVT control senses the starting of the engine. In particular, the determination on the cam torque response control mode under a condition of open loop response time (OLRT) at 100° (crank angle)/sec, an engine RPM equal to or less than 1000 RPM, and an oil temperature of 110° C. to 130° C., which are engine driving conditions to increase an emission effect for reducing harmful substances, is carried out.

In detail, the cam torque response control mode (S30 to S140) is divided into steps of: checking a first fast unlocking condition in which responsiveness of the middle phase CVVT is reduced due to an unlocking switching delay of a lock pin which locks the cam at a middle position in the middle phase CVVT (S30 to S50); checking a second fast unlocking condition in which a flow of oil supplied to the lock pin for lock pin chattering is changed (S70 to S110); and performing a cam torque response control to prevent the responsiveness of the middle phase CVVT from increasing by rapidly unlocking the lock pin using the lock pin chattering (S120 to S140).

The first fast unlocking condition includes conditions of an oil temperature, an engine RPM, and a voltage. In detail, the oil temperature is set to be oil temperature>TH_(—)0 in step S30, and the first fast unlocking condition checking is continuously performed when the conditions are satisfied. Here, the TH_(—)0 is an oil temperature threshold Threshold_Oil, and when the oil temperature=110° C. to 130° C., it is represented as TH_(—)0<110° C. to 130° C. In step S40, the engine RPM is applied as engine RPM<TH_R. When the conditions are satisfied, the first fast unlocking condition checking is continuously performed. Here, the TH_R is an engine RPM threshold Threshold_RPM, and when the engine RPM=500 RPM to 1000 RPM, it is represented as TH_R>1000 RPM. In step S50, the voltage is applied as voltage<TH_L, and the first fast unlocking condition checking ends when the conditions are satisfied. Here, the TH_L, which is a voltage threshold Threshold_Low, represents a voltage applied to an oil-flow control valve (OCV), and therefore, a magnitude in the applied voltage is different according to an OCV specification, and therefore is not limited to a specific value.

Therefore, in the first fast unlocking condition, after the determination on oil temperature>TH_(—)0, engine RPM<TH_R, and voltage<TH_L are sequentially performed and all the conditions are satisfied, the step of entering the cam torque response control mode is performed (S60), and then, the checking of the second fast unlocking condition is performed.

The second fast unlocking condition includes a crank, an intake valve, a cam, oil, and a cam torque phase. In step S70, crank signal synchronization is checked, and in step S80, an opening timing of the intake valve for each cylinder is differentiated. In step S90, a cam torque is determined, and in step S100, the oil temperature divided into a first oil temperature of a region of 110° C. and a second oil temperature of a region of 130° C. is checked. In step S110, a negative cam torque and a positive cam torque are differentiated.

Therefore, in the second fast unlocking condition, the sequential check for the crank signal synchronization, the opening timing of the intake valve for each cylinder, and the cam torque is performed. Then, under the first oil temperature condition of the region of 110° C., the cam torque response control is performed when the negative cam torque is generated, or under the second oil temperature condition of the region of 130° C., the cam torque response control is performed when the negative cam torque is generated (S120).

In accordance with the exemplary embodiment of the present inventive concept, the cam torque response control is performed in step S120 when the intake valve opens. Referring to FIG. 2, the positive cam torque is generated when a cam phase of a cam shaft receiving a rotation of the crank shaft by engine combustion through a chain (or belt) closes the intake valve, while the negative cam torque is generated when the intake valve opens.

The cam torque response control of S120 is rapidly performed by selecting a duty cycle for controlling the cam torque as in S130 and then transmitting the duty cycle to a cam phaser control stage as in S140. In this case, cam torque control duty cycle of S130 is determined to be equal to F(X), and thus, a value of the duty cycle is defined as the oil temperature read in S100.

FIG. 3 illustrates an operation of the middle phase CVVT receiving an output of the cam phaser control stage of S140. As illustrated, the output of the cam phaser control stage is transmitted to an oil-flow control valve (OCV) 10-1 as a pulse width modulation (PWM) duty signal. In this case, the output of the cam phaser control stage is generated when the negative cam torque is generated, and thus, the OCV 10-1 is repeatedly turned on/off. Then, the oil flow in a lock pin 10-4 installed on an oil pressure circuit 10-2 connecting a cam 10-3 to the OCV 10-1 can be repeatedly intermitted by turning on/off the OCV 10-1. As a result, the lock pin chattering is generated in the lock pin 10-4 which maintains the cam 10-3 as a middle position locking (or detent) state and thus is rapidly switched to an unlocking state (locking→unlocking). As a result, the cam 10-3 is rapidly switched to an advanced position or a retarded position without being restricted by the lock pin 10-4, and thus, a responsiveness delay which may occur since the lock pin 10-4 is completely prevented in the middle phase CVVT.

Further, FIG. 4 illustrates control performance of the middle phase CVVT when rapidly unlocking the lock pin due to the lock pin chattering. As illustrated in FIG. 4, when an emission effect reference line A is a condition of an open loop response time (OLRT) at 100° (crank angle)/sec, the lock pin 10-4 is rapidly unlocked due to the lock pin chattering in a cam torque response control C at the oil temperature of 110° C. and a cam torque response control D at the oil temperature of 130° C., respectively, and thus, it is confirmed that a response delay region B is not generated even at a low-speed engine RPM equal to or less than 500 to 1000 RPM.

Referring to FIGS. 1A and 1B, the cam phaser control mode (S200 and S300) is entered when the first fast unlocking condition checked in the steps of determining the lock pin chattering (S30 to S50) is not established and when the second fast unlocking condition checked in the steps of entering the lock pin chattering (S70 to S110) is not established.

For example, when non-established conditions of the first fast unlocking condition are oil temperature>TH_(—)0, engine RPM<TH_R, and voltage<TH_L, the entering of the cam phaser control mode (S200) is performed. In this case, oil temperature>TH_(—)0, engine RPM<TH_R, and voltage<TH_L is applied. Further, when a non-established condition of the second fast unlocking condition is a case in which the cam torque phase is the positive cam torque, the entering of the cam phaser control mode (S200) is performed.

Next, the cam phaser control is performed by the entering of the cam phaser control mode in S300. The cam phaser control mode represents that the PWM duty signal transmitted from the cam phaser control stage to the OCV 10-1 is made depending on the difference between the target value of the cam and the current value of the cam, which means a normal control state of the middle phase CVVT.

FIGS. 5A and 5B illustrate a configuration example of the middle phase CVVT 10 controlled by a controller 110 to perform a dual middle phase control in accordance with the exemplary embodiment of the present inventive concept.

As illustrated in FIG. 5B, the middle phase CVVT 10 includes the oil-flow control valve (OCV) 10-1 configured to control an engine oil flow and an influx delivered to the cam 10-3 by the PWM duty control. An oil pressure circuit 10-2 is formed between the cam 10-3 and the OCV 10-1 to circulate an oil. The cam 10-3 supplies the oil from the oil pressure circuit 10-2. The lock pin 10-4 is disposed in the oil pressure circuit 10-2 connected to the cam 10-3 to perform the middle position locking (or detent) of the cam 10-3 and an advanced position or the retarded position switching. Therefore, the oil flow and the influx at the time of the cam torque response control mode are changed by repeatedly turning on/off the OCV 10-1, and thus, the lock pin chattering may occur in the lock pin 10-4.

In accordance with the exemplary embodiment of the present inventive concept, the middle phase CVVT 10 controls a cam 10-3 position at the most retarded (intake) position or the most advanced (exhaust) position, with the oil temperature of −10° C. to 130° C. and the engine RPM equal to or more than 500 RPM.

Further, the controller 110 precisely controls the middle phase by an internal oil passage, and an oil supply to an advanced/retarded chamber, and in particular, the turn on/off of the PWM duty signal which may rapidly unlock the lock pin 10-4 by the lock pin chattering.

Referring to FIG. 5A, the controller 110 includes a cam torque sensor 110-1, a cam phaser control determiner 110-2, a cam torque control determiner 110-3, and a cam phaser controller 120. The cam torque sensor 110-1, the cam phaser control determiner 110-2, and the cam torque control determiner 110-3 are integrated into a single block so that each output line is connected to the cam phaser controller 120.

In detail, a cam torque sensing data 110-1A is input to the cam torque sensor 110-1, and the cam torque and the negative/positive cam torque phase are determined based on the cam torque sensing data 110-1A, and thus, an execution timing of the cam torque response control mode (S30 to S140) is output to the cam phaser controller 120. The cam torque sensing data 110-1A includes a crank signal, a cooling water temperature, and an OCV voltage. A cam phaser control data 110-2A is input to the cam phaser control determiner 110-2, and the difference between the target value of the cam and the current value of the cam for the cam phaser control mode (S200 and S300) is calculated based on the cam phaser control data 110-2A, and thus, a control value of the cam phaser control mode (S200 and S300) is output to the cam phaser controller 120. An oil temperature data 110-3A is input to the cam torque control determiner 110-3, and the oil temperature is divided into 100° C. and 130° C. based on the oil temperature data 110-3A. Thus, the control value of the cam torque response control mode (S30 to S140) is divided into a 110° C. oil temperature control value and a 130° C. oil temperature control value, the control value of the cam torque response control mode is then output to the cam phaser controller 120. The cam phaser controller 120 outputs the PWM duty signal transmitted to the OCV 10-1 as an electrical signal.

In accordance with the exemplary embodiment of the present inventive concept, as the controller 110, a dedicated controller specified to control the middle phase CVVT 10 or an engine control unit (ECU) or an electric control unit controlling the engine may be applied.

As described above, in the continuously variable valve timing system with intermediate lock pin and cam torque response control, the response delay of the lock pin causing the responsiveness reduction of the middle phase CVVT under the condition of the open loop response time (OLRT) at 100° (crank angle)/sec, the engine RPM equal to or less than 1000 RPM, and the oil temperature of 110° C. to 130° C. is solved by checking the conditions of the oil temperature>TH_(—)0, the engine RPM<TH_R, and the voltage<TH_L in which the responsiveness of the middle phase CVVT is reduced due to the unlocking switching delay of the lock pin 10-4 which locks the cam 10-3 at the middle position, checking the cam torque phase condition for the lock pin chattering, and then when the conditions are satisfied, rapidly switching the lock pin 10-4 to the unlocking state (locking→unlocking) using the lock pin chattering and the required operation functions of the middle phase CVVT at the oil temperature of −10° C. to 130° C. and the engine RPM equal to or less than 500 RPM are completely satisfied by preventing the responsiveness of the middle phase CVVT from reducing.

In accordance with the exemplary embodiments of the present inventive concept, it is possible to to reduce the control responsiveness of the middle phase CVVT under the condition of the open loop response time (OLRT) at 100° (crank angle)/sec, the engine RPM equal to or less than 1000 RPM, and the oil temperature of 110° C. to 130° C. by rapidly performing the unlocking using the lock pin chattering by the oil pressure flow control after the middle phase locking of the cam by the lock pin at the time of controlling the middle phase of the cam.

Further, in accordance with the exemplary embodiments of the present inventive concept, it is possible to rapidly perform the locking/unlocking of the lock pin by implementing the lock pin chattering by turning on/off the oil-flow control valve using the pulse width modulation (PWM) control command.

In addition, in accordance with the exemplary embodiments of the present inventive concept, it is possible to use two cam torque control modes which are a positive cam torque control mode and a negative cam torque control mode by performing the PWM control command for reducing the response delay of the lock pin using the negative cam torque control mode generated when the intake valve opens.

Furthermore, in accordance with the exemplary embodiments of the present inventive concept, it is possible to provide the middle phase CVVT capable of satisfying required operation functions with the oil temperature of −10° C. to 130° C. and the engine RPM equal to or more than 500 RPM by preventing the occurrence of the response delay due to the unlocking delay of the lock pin at the time of controlling the middle phase and easily cope with the strict environmental regulations demanding the exhaust gas reduction and the fuel efficiency and performance improvement by applying the middle phase CVVT to a vehicle. 

What is claimed is:
 1. A method of controlling an intermediate lock pin and cam torque response for a middle phase continuously variable valve timing (CVVT) system, the method comprises steps of: entering a cam phaser control mode for controlling the middle phase CVVT when an engine starts, or performing lock pin chattering of a lock pin locking a cam at a middle position, which is a position between an advanced position and a retarded position, by an oil pressure; and entering a cam torque response control mode for controlling the middle phase CVVT, wherein the lock pin chattering occurs due to an intermittent oil flow supplying to the lock pin.
 2. The method of claim 1, wherein the intermittent oil flow is formed by intermittently turning on/off an oil-flow control valve (OCV) which controls the oil.
 3. The method of claim 1, wherein the cam torque response control mode is entered when a target value of the cam is the same as a current value of the cam and the cam phaser control mode is entered when the target value of the cam is different from the current value of the cam.
 4. The method of claim 3, wherein an execution condition of the cam torque response control mode includes an engine revolutions per minute (RPM) of 500 to 1000 RPM and an oil temperature of 110° C. to 130° C.
 5. The method of claim 4, wherein the execution condition of the cam torque response control mode further includes an open loop response time (OLRT) at 100° (crank angle)/sec for an emission effect.
 6. The method of claim 1, wherein the cam torque response control mode is executed by steps of: determining whether an unlocking of the lock pin is delayed by a first fast unlocking condition; determining whether the lock pin chattering is performed by a second fast unlocking condition after the delay of unlocking the lock pin is determined; and performing the lock pin chattering by controlling the cam torque response when controlling the middle phase CVVT.
 7. The method of claim 6, wherein the first fast unlocking condition includes an oil temperature, an engine RPM, and a voltage.
 8. The method of claim 7, wherein determination conditions of the first fast unlocking includes oil temperature>TH_(—)0 (oil temperature threshold), engine RPM<TH_R (engine RPM threshold), and voltage<TH_L (voltage threshold), and the unlocking delay of the lock pin is determined when all the determination conditions are satisfied.
 9. The method of claim 8, wherein the oil temperature is 110° C. to 130° C., the engine RPM is 500 RPM to 1000 RPM, and the voltage is a voltage of an oil-flow control valve (OCV) controlling the oil of the middle phase CVVT.
 10. The method of claim 8, further comprising a step of: terminating the unlocking delay determination of the lock pin and entering the cam phaser control mode for performing the control of the middle phase CVVT when any one of the determination condition of the oil temperature, the determination condition of the engine RPM, and the determination condition of the voltage is not satisfied.
 11. The method of claim 6, further comprising steps of: determining the lock pin chattering when a negative cam torque is generated and an intake valve opens; and dividing the oil temperature into a first oil temperature of a region of 110° C. and a second oil temperature of a region of 130° C., and performing the lock pin chattering at the first oil temperature and the second oil temperature, respectively, wherein the second fast unlocking condition includes crank signal synchronization, an opening timing determination of the intake valve for each cylinder, a cam torque determination, an oil temperature check, and a cam torque phase determination.
 12. The method of claim 11, further comprising a step of: terminating the lock pin chattering and entering the cam phaser control mode for immediately performing the control of the middle phase CVVT when a positive cam torque is generated and the intake valve closes.
 13. The method of claim 6, wherein in the cam torque response control, the lock pin chattering is a pulse width modulation (PWM) duty signal supplied to an OCV, in which the PWM duty signal is divided into a first oil temperature of a region of 110° C. and a second oil temperature of a region of 130° C. under the second fast unlocking condition, and an output of the PWM duty signal is generated at a negative cam torque phase when the intake valve opens under the second fast unlocking condition.
 14. A middle phase continuously variable valve timing (CVVT) system, the system comprising: a controller configured to control a middle phase CVVT when an engine runs, the controller including: a cam torque sensor, a cam phaser control determiner, a cam torque control determiner, and a cam phaser controller, wherein the cam torque sensor is configured to use a crank signal, a cooling water temperature, an oil-flow control valve (OCV) voltage as a cam torque sensing data, configured to detect a cam torque phase by a negative cam torque generated when an intake valve opens and a positive cam torque generated when the intake valve closes, and configured to output a negative cam torque signal to the cam phaser controller, the cam phaser control determiner is configured to use a difference between a target value of a cam and a current value of the cam calculated based on the cam torque as a cam phaser control data and configured to output the signal based on the difference between the target value of the cam and the current value of the cam to the cam phaser controller, the cam torque control determiner is configured to use an oil temperature for oil temperature data, is configured to divide the oil temperature into a first oil temperature and a second oil temperature, and configured to output the divided oil temperature to the cam phaser controller, and the cam phaser controller configured to output a pulse width modulation (PWM) duty signal generated by the first oil temperature and the second oil temperature when the cam torque phase is a negative phase and configured to output the PWM duty signal to the OCV controlling an oil of the middle phase CVVT.
 15. The middle phase CVVT system of claim 14, wherein the OCV is connected to an oil pressure circuit, and the oil pressure circuit is connected to the cam which controls an intake valve and an exhaust valve, the oil pressure circuit is provided with a lock pin locking the cam at a middle position between a most retarded position and a most advanced position, and lock pin chattering is generated in the lock pin by repeatedly turning on/off the OCV by the PWM duty signal.
 16. The middle phase CVVT system of claim 15, wherein the OCV controls the oil at an oil temperature of −10° C. to 130° C. and an engine RPM equal to or more than 500 RPM.
 17. The middle phase CVVT system of claim 14, wherein the cam torque sensor, the cam phaser control determiner, and the cam torque control determiner are integrated into a single block so that each output line is connected to the cam phaser controller.
 18. The middle phase CVVT system of claim 14, wherein the controller is an engine control unit (ECU) controlling the engine.
 19. The middle phase CVVT system of claim 14, wherein the first oil temperature is in a region of 110° C., and the second oil temperature is in a region of 130° C.
 20. A non-transitory computer-readable recording medium comprising computer executable instructions which cause a controller to perform the method according to claim
 1. 